The removal of reinforced concrete and/or various other corrosion-protective coatings from and about an underwater structure, such as a pipeline, is particularly difficult and labor intensive. There have been numerous experiences of structural damage during the process of removing such coatings, particularly by divers in the preparation of underwater structural connections. A gouged, scored, or partially cut structure serves as a stress concentration point which potentially could lead to a structural weakening or failure.
In the case of deepwater pipelines, it is essential that some type of remote inspection system be employed to remove coatings and effect repairs to the pipe inasmuch as such working depths may be below ordinary diver inspection capabilities. The use of a saw for removing concrete coatings requires that the thickness of the concrete be determined prior to inserting the concrete cutting device and, when initiated, continuously monitored throughout the cutting process in order to avoid damage to the pipeline. It is known in the art that a magnetometer device may be employed to detect reinforcing bars in concrete and to determine the approximate thickness of the concrete cover over the bars within accuracy limitations (James Electronics, Inc., "Application and Operating Manual" for Model C-4952 "R" Meter). However, the situation becomes more complicated in the case of pipelines or other metallic structural shapes that must be protected from damage and which may be covered with concrete containing embedded mesh or wire reinforcements. The magnetometer device of the prior art is not capable of "seeing through or ignoring" embedded magnetic materials or the removal mechanism in order to "see or detect" the primary structure itself--in this case, the pipe.
Accordingly, the present invention, in answer to this need in the art, provides an integrating electromagnetic sensor device and method for use thereof, capable of detecting the thickness of a pipe covering membrane about a pipe--the covering membrane, potentially, also containing magnetic aggregates in addition to embedded magnetic reinforcements.